The fact about the P67 motherboard needing an extra 3D card is correct. I’m not sure why (intel must have their reasons):
P67 - Chipset provides enhanced overclocking features that allow you to mess with the multiplier a lot more. No facility to use the onboard GPU.
H67 - Limited overclock but has the bits needed to use the onboard GPU.
The Sandybridge chips themselves house the GPU, they are what is known as APU’s now (CPU+GPU). If you want to use the onboard graphics you will need to buy a H67 board but unfortunately that will limit the potential of that i5-2500K as you won’t be able to overclock it much.
Save the extra few dollars and get something for in between is my advice. Something like a 5570 or 5670 if you can find one cheap enough, should be $80 max for the 5670.